Styela clava and its cousin Styela plicata have been getting some pretty bad press over the last 10 years due to their circumglobal distribution and classification as Marine Invasive Species. As a Styela biologist, I'd like to spend some time discussing some of the positive aspects to the Styela story. They may be be ugly ducklings on the outside (literally), but because of their recent world-wide distribution, they have also been the subject of scientific investigation by several research labs. They are an attractive research model because they are readily available to researchers around the temperate world (in both hemispheres), and they are an important group of ascidians biologically in terms of their relationships to colonial botryllid species and other solitary ascidians. In Asia (Korea), S. clava is part of the regional cuisine (Mideodok-chim) and is grown in aquaculture. The biology of Styela has become important for understanding diseases that have threatened commercially-cultured ascidians (soft-tunic syndrome in Halocynthia roretzi). Inside, they are fascinating to study because their internal organs are bright orange and easy to examine. S. clava is particularly useful because it is slender with a relatively thin, easily-cut tunic, whereas S. plicata is globular in shape and has a thick, less pliable tunic. S. clava cohabitates with S. plicata in bays where their ranges overlap on both the East and West US coasts.
Native American Styelids (Pacific Coast): S. montereyensis, and S. gibbssi.
Diagram of the internal organs of Styela clava
Styela clava has a number of advantages as a model system for the study of solitary ascidians. It is abundant, grows up to 4-5 inches (12 cm), and is easy to dissect. It is adaptable for a wide range of studies and has a firm, flexible tunic that supports the internal organs during dissection. In coastal marinas, S. clava individuals on docks show a range of sizes depending on the season and whether the substrate has been recently cleared. During my 2011 MIS monitoring from Cape Cod to Salem Harbor, the population density was kept at a moderate level by competition with other encrusting invertebrates and colonial ascidian species, especially Didemnum vexillum and Diplosoma listerianum, which can aggressively overgrow solitary ascidians. When fully mature, large individuals are easy to spot (unless totally covered by Didemnum). However, small, young individuals may not be counted in the field when if they are not recognized. This is particularly important in marinas with new or cleaned docks.
WEB AND LITERATURE SEARCH TERMS:
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